Inhibition of the mammary carcinoma angiogenic switch in C3(1)/SV40 transgenic mice by a mutated form of human endostatin

Efficient targeted tumor imaging and secreted endostatin gene delivery by anti-CD105 immunoliposomes

BACKGROUND

Anti-CD105 mAb-conjugated immunoliposomes, loaded with secreted mouse endostatin gene, were developed for targeted tumor imaging and antiangiogenic gene therapy.

METHODS

The liposomes were investigated for size, zeta-potential, lipid content, antibody binding ability, and pcDNA loading capacity. The ability of immunoliposomes to target tumor-derived endothelial cells and perform gene transfer in vitro was measured and their basic biocompatibility was evaluated. A nude mouse/breast cancer xenograft model was used to examine the tumor internalization of fluorescent-labeled liposomes and the clinical potential of immnuoliposomes loaded with pcDNA3.1-CSF1-endostatin.

RESULTS

Loaded immunoliposomes were homogenously distributed with a well-defined spherical shape and bilayer, diameter of 122 ± 11 nm, and zeta potential + 1.40 mV. No significant differences were observed in body weight, liver index, oxidative stress, or liver and kidney function in mice after liposomes exposure. The addition of CD105 mAb to liposomes conferred the ability to target tumor-derived endothelial cells in vitro and in vivo. Systemic intravenous administration of fluorescent immunoliposomes in the xenograft model resulted in selective and efficient internalization in tumor vasculature. Treatment of mice with pcDNA3.1-CSF1-endostatin-loaded immunoliposomes suppressed tumor growth by 71%.

CONCLUSIONS

These data demonstrate the advantages of using anti-CD105 mAb-conjugated immunoliposomes to enhance tumor targeting, imaging, and gene transfer applications.

Effect of Endostatin on Preventing Postoperative Progression of Distant Metastasis in a Murine Lung Cancer Model

Aims and Background

The relapse and metastasis of cancer remain a predominant cause of death after surgical removal of the primary tumor. There is a positive linkage between the postoperative upregulation of systemic angiogenic activity and distant tumor metastasis. In the present study, we established a spontaneous metastasis model and investigated whether antiangiogenic therapy using endostatin could prevent the progression of distant metastasis after removal of the primary tumor.

Methods

Female C57BL/6 mice were implanted subcutaneously with 1 × 106 Lewis lung cancer cells. Twenty days after implantation of the cancer cells, the primary tumor was removed and the mice were randomly divided into three groups. The NS group received normal saline, the L-ES group received 3 mg/kg endostatin, and the H-ES group received 20 mg/kg endostatin intravenously daily for 10 days. The effect of endostatin on lung metastases and the survival time of the mice were observed. Flow cytometry and immunohistochemistry were carried out to assess the angiogenic activity. The serum endostatin levels in peripheral blood were measured using an enzyme-linked immunosorbent assay.

Results

The mean number of metastatic pulmonary nodules and the mean net lung weight in the NS, L-ES and H-ES groups was 10.2, 2.8 and 4.0, and 0.55g, 0.31g and 0.36g, respectively. The difference between the NS group and the endostatin-treated groups was statistically significant (P <0.05). The endostatin-treated mice showed prolonged overall survival (P <0.05). Compared with the NS group, the endostatin-treated groups had lower levels of circulating endothelial cells in peripheral blood and showed a decrease in microvessel density in the metastatic tumors, with a more marked reduction in the L-ES group (P <0.05). The systemic presence of endostatin was gradually increased with the continued administration of endostatin to the mice.

Conclusions

Antiangiogenic therapy with endostatin is effective in inhibiting the postoperative progression of distant metastasis.

Development and Preclinical Application of an Immunocompetent Transplant Model of Basal Breast Cancer with Lung, Liver and Brain Metastases

Triple negative breast cancer (TNBC) is an aggressive subtype of breast cancer that is associated with a poor prognosis and for which no targeted therapies currently exist. In order to improve preclinical testing for TNBC that relies primarily on using human xenografts in immunodeficient mice, we have developed a novel immunocompetent syngeneic murine tumor transplant model for basal-like triple-negative breast cancer. The C3(1)/SV40-T/t-antigen (C3(1)/Tag) mouse mammary tumor model in the FVB/N background shares important similarities with human basal-like TNBC. However, these tumors or derived cell lines are rejected when transplanted into wt FVB/N mice, likely due to the expression of SV40 T-antigen. We have developed a sub-line of mice (designated REAR mice) that carry only one copy of the C3(1)/Tag-antigen transgene resulting from a spontaneous transgene rearrangement in the original founder line. Unlike the original C3(1)/Tag mice, REAR mice do not develop mammary tumors or other phenotypes observed in the original C3(1)/Tag transgenic mice. REAR mice are more immunologically tolerant to SV40 T-antigen driven tumors and cell lines in an FVB/N background (including prostate tumors from TRAMP mice), but are otherwise immunologically intact. This transplant model system offers the ability to synchronously implant the C3(1)/Tag tumor-derived M6 cell line or individual C3(1)/Tag tumors from various stages of tumor development into the mammary fat pads or tail veins of REAR mice. C3(1)/Tag tumors or M6 cells implanted into the mammary fat pads spontaneously metastasize at a high frequency to the lung and liver. M6 cells injected by tail vein can form brain metastases. We demonstrate that irradiated M6 tumor cells or the same cells expressing GM-CSF can act as a vaccine to retard tumor growth of implanted tumor cells in the REAR model. Preclinical studies performed in animals with an intact immune system should more authentically replicate treatment responses in human patients.

Endostatin and endorepellin: A common route of action for similar angiostatic cancer avengers

Traditional cancer therapy typically targets the tumor proper. However, newly-formed vasculature exerts a major role in cancer development and progression. Autophagy, as a biological mechanism for clearing damaged proteins and oxidative stress products released in the tumor milieu, could help in tumor resolution by rescuing cells undergoing modifications or inducing autophagic-cell death of tumor blood vessels. Cleaved fragments of extracellular matrix proteoglycans are emerging as key players in the modulation of angiogenesis and endothelial cell autophagy. An essential characteristic of cancer progression is the remodeling of the basement membrane and the release of processed forms of its constituents. Endostatin, generated from collagen XVIII, and endorepellin, the C-terminal segment of the large proteoglycan perlecan, possess a dual activity as modifiers of both angiogenesis and endothelial cell autophagy. Manipulation of these endogenously-processed forms, located in the basement membrane within tumors, could represent new therapeutic approaches for cancer eradication.

Dose-dependent benefits of quercetin on tumorigenesis in the C3(1)/SV40Tag transgenic mouse model of breast cancer

Breast cancer is the leading cause of cancer related death in women. Quercetin is a flavonol shown to have anti-carcinogenic actions. However, few studies have investigated the dose-dependent effects of quercetin on tumorigenesis and none have used the C3(1)/SV40 Tag breast cancer mouse model. At 4 weeks of age female C3(1)/SV40 Tag mice were randomized to one of four dietary treatments (n = 15-16/group): control (no quercetin), low-dose quercetin (0.02% diet), moderate-dose quercetin (0.2% diet), or high-dose quercetin (2% diet). Tumor number and volume was assessed twice a week and at sacrifice (20 wks). Results showed an inverted 'U' dose-dependent effect of dietary quercetin on tumor number and volume; at sacrifice the moderate dose was most efficacious and reduced tumor number 20% and tumor volume 78% compared to control mice (C3-Con: 9.0 ± 0.9; C3-0.2%: 7.3 ± 0.9) and (C3-Con: 2061.8 ± 977.0 mm(3); and C3-0.2%: 462.9 ± 75.9 mm(3)). Tumor volume at sacrifice was also reduced by the moderate dose compared to the high and low doses (C3-2%: 1163.2 ± 305.9 mm(3); C3-0.02%: 1401.5 ± 555.6 mm(3)), as was tumor number (C3-2%: 10.7 ± 1.3 mm(3); C3-0.02%: 8.1 ± 1.1 mm(3)). Gene expression microarray analysis performed on mammary glands from C3-Con and C3-0.2% mice determined that 31 genes were down-regulated and 9 genes were up-regulated more than 2-fold (P < 0.05) by quercetin treatment. We report the novel finding that there is a distinct dose-dependent effect of quercetin on tumor number and volume in a transgenic mouse model of human breast cancer, which is associated with a specific gene expression signature related to quercetin treatment.

Targeted antiangiogenesis gene therapy using targeted cationic microbubbles conjugated with CD105 antibody compared with untargeted cationic and neutral microbubbles

Objective This study aimed to develop targeted cationic microbubbles conjugated with a CD105 antibody (CMB105) for use in targeted vascular endothelial cell gene therapy and ultrasound imaging. We compared the results with untargeted cationic microbubbles (CMB) and neutral microbubbles (NMB).

Methods CMB105 were prepared and compared with untargeted CMB and NMB. First, the microbubbles were characterized in terms of size, zeta-potential, antibody binding ability and plasmid DNA loading capacity. A tumor model of subcutaneous breast cancer in nude mice was used for our experiments. The ability of different types of microbubbles to target HUVECs in vitro and tumor neovascularization in vivo was measured. The endostatin gene was selected for its outstanding antiangiogenesis effect. For in vitro experiments, the transfection efficiency and cell cycle were analyzed using flow cytometry, and the transcription and expression of endostatin were measured by qPCR and Western blotting, respectively. Vascular tube cavity formation and tumor cell invasion were used to evaluate the antiangiogenesis gene therapy efficiency in vitro. Tumors were exposed to ultrasound irradiation with different types of microbubbles, and the gene therapy effects were investigated by detecting apoptosis induction and changes in tumor volume.

Results CMB105 and CMB differed significantly from NMB in terms of zeta-potential, and the DNA loading capacities were 16.76±1.75 μg, 18.21±1.22 μg, and 0.48±0.04 μg per 5×10⁸ microbubbles, respectively. The charge coupling of plasmid DNA to CMB105 was not affected by the presence of the CD105 antibody. Both CMB105 and CMB could target to HUVECs in vitro, whereas only CMB105 could target to tumor neovascularization in vivo. In in vitro experiments, the transfection efficiency of CMB105 was 24.7-fold higher than the transfection efficiency of NMB and 1.47-fold higher than the transfection efficiency of CMB (P<0.05). With ultrasound-targeted microbubble destruction (UTMD)-mediated gene therapy, the transcription and expression of endostatin were the highest in the CMB105 group (P<0.001); the antiangiogenesis effect and inhibition of tumor cells invasion was better with CMB105 than CMB or NMB in vitro (P<0.01). After gene therapy, the tumor volumes of CMB105 group were significantly smaller than that of CMB and NMB, and many tumor cells had begun apoptosis in the CMB105 group, which had the highest apoptosis index (P<0.001).

Conclusions As a contrast agent and plasmid carrier, CMB105 can be used not only for targeted ultrasound imaging but also for targeted gene therapy both in vitro and in vivo. The plasmid DNA binding ability of the CMB was not affected by conjugation of the CMB with the CD105 antibody, and because of its targeting ability, the gene transfection efficiency and therapeutic effect were better compared with the untargeted CMB and NMB. The advantages of targeted gene therapy with CMB105 in vivo were more prominent than with CMB or NMB because neither can target the endothelia in vivo.

Effects of the MCP-1 synthesis inhibitor bindarit on tumorigenesis and inflammatory markers in the C3(1)/SV40Tag mouse model of breast cancer

Breast cancer, the most deadly cancer in women, is characterized by elevated levels of inflammation within and surrounding the tumor, which can lead to accelerated growth, invasion and metastasis. Macrophages are central to the inflammatory milieu and are recruited to the tumor microenvironment by several factors including monocyte chemoattractant protein-1 (MCP-1). Using the anti-inflammatory molecule bindarit to target MCP-1, we investigated the role of this chemokine on macrophage related inflammation and mammary tumorigenesis in a transgenic mouse model of breast cancer. C3(1)/SV40Tag mice and wild type FVB/N were randomized to either control or 0.5% bindarit diet from 4 to 21weeks of age. Tumor number and volume were recorded over time and at sacrifice. Macrophage markers as well as inflammatory meditators were examined in the tumor tissue and mammary glands. Circulating MCP-1 and IL-6 were measured by ELISA. Bindarit treatment reduced tumor number (P<0.05), but did not affect tumor size, tumor weight or tumor latency in C3(1)/SV40Tag mice. Within the tumor, mRNA expression of bindarit's primary targets, MCP-1 and IL-12/p35, were significantly decreased by bindarit treatment (P<0.05), and this was consistent with trends for reduced expression of TNF-α, IL-6, F4/80, CD206, and IL-10. In mammary tissue, expression of MCP-1, TNF-α, IL-6, F4/80, IL-10 and IL-12/p35 was significantly elevated in C3(1)/SV40Tag mice compared to wild type FVB/N mice, but IL-6 was the only marker decreased by bindarit treatment (P<0.05). Plasma MCP-1 was highly correlated with tumor volume (P<0.05); however, it was not affected by bindarit at 21weeks of age. Similarly, circulating IL-6 was increased in C3(1)/SV40Tag mice but there was no effect of bindarit treatment. These results show that tumor multiplicity in the C3(1)/SV40Tag mouse model of breast cancer is reduced by bindarit, however these effects are independent of changes in plasma levels of MCP-1 and IL-6, but may be related to the attenuated expression of MCP-1 along with several inflammatory mediators and macrophage markers within the tumor.

STX140, but not paclitaxel, inhibits mammary tumour initiation and progression in C3(1)/SV40 T/t-antigen transgenic mice

Despite paclitxael's clinical success, treating hormone-refractory breast cancer remains challenging. Paclitaxel has a poor pharmacological profile, characterized by a low therapeutic index (TIX) caused by severe dose limiting toxicities, such as neutropenia and peripheral neuropathy. Consequently, new drugs are urgently required. STX140, a compound previously shown to have excellent efficacy against many tumors, is here compared to paclitaxel in three translational in vivo breast cancer models, a rat model of peripheral neuropathy, and through pharmacological testing. Three different in vivo mouse models of breast cancer were used; the metastatic 4T1 orthotopic model, the C3(1)/SV40 T-Ag model, and the MDA-MB-231 xenograft model. To determine TIX and pharmacological profile of STX140, a comprehensive dosing regime was performed in mice bearing MDA-MD-231 xenografts. Finally, peripheral neuropathy was examined using a rat plantar thermal hyperalgesia model. In the 4T1 metastatic model, STX140 and paclitaxel significantly inhibited primary tumor growth and lung metastases. All C3(1)/SV40 T-Ag mice in the control and paclitaxel treated groups developed palpable mammary cancer. STX140 blocked 47% of tumors developing and significantly inhibited growth of tumors that did develop. STX140 treatment caused a significant (P<0.001) survival advantage for animals in early and late intervention groups. Conversely, in C3(1)/SV40 T-Ag mice, paclitaxel failed to inhibit tumor growth and did not increase survival time. Furthermore, paclitaxel, but not STX140, induced significant peripheral neuropathy and neutropenia. These results show that STX140 has a greater anti-cancer efficacy, TIX, and reduced neurotoxicity compared to paclitaxel in C3(1)/SV40 T-Ag mice and therefore may be of significant benefit to patients with breast cancer.

[Integrins as a potential target for targeted anticancer therapy]

The review briefly summarizes information of structure of integrins and their involvement in the development and malignant progression of tumors. Special attention is paid to approaches based on modification of functional properties of integrins that prevent/antagonize tumor growth and progression; these approaches developed in modem experimental biology have certain perspective in clinical application.

Targeted delivery of an antibody-mutant human endostatin fusion protein results in enhanced antitumor efficacy

The antiangiogenic protein endostatin showed considerable preclinical antitumor activity, but limited efficacy in phase I/II trials. Prior studies using an anti-HER2 antibody-murine endostatin fusion showed enhanced antitumor activity compared to anti-HER2 antibody or endostatin given alone, or in combination. We have generated two anti-HER2 human endostatin fusion proteins by fusing either wild-type or a mutant human endostatin (huEndo-P125A) to the 3' end of a humanized anti-HER2 IgG3 antibody. Antitumor efficacy was examined in murine and human breast tumor models. HuEndo-P125A antibody fusion protein (αHER2-huEndo-P125A) inhibited VEGF and bFGF induced endothelial cell proliferation, and tube formation in vitro, more efficiently than endostatin alone, wild-type endostatin fusion protein (αHER2-huEndo), or parental anti-HER2 antibody (αHER2 IgG3). Wild-type and mutant human endostatin was rapidly cleared from serum in mice (T½(2) = 2.0-2.1 hours), whereas αHER2-huEndo fusion proteins had a significantly prolonged half-life (T½(2) = 40.7-57.5 hours). Treatment of SK-BR-3 breast cancer xenografts with anti-HER2 IgG3-huEndo-P125A fusion resulted in greater inhibition of tumor growth and improved survival, compared to treatment with either αHER2 IgG3 (P = 0.025), human endostatin (P = 0.034), or anti-HER2 IgG3-huEndo (P = 0.016). αHER2-huEndo-P125A specifically inhibited tumors expressing HER2 in mice simultaneously implanted with murine mammary tumor EMT6 cells and with EMT6 engineered to express HER2 antigen (EMT6-HER2). Targeting of endostatin using antibody fusion proteins could improve antitumor activity of either anti-HER2 antibody and/or endostatin and provides a versatile approach that could be applied to other tumor targets with alternative antibody specificities.

Magnetic resonance imaging of the natural history of in situ mammary neoplasia in transgenic mice: a pilot study

Introduction

Because of the small size of in situ mammary cancers in mouse models, high-resolution imaging techniques are required to effectively observe how lesions develop, grow and progress over time. The purpose of this study was to use magnetic resonance (MR) imaging to track in vivo the transition from in situ neoplasia to invasive cancer in a transgenic mouse model of human cancer.

Methods

MR images of 12 female C3(1) SV40 Tag mice that develop mammary intraepithelial neoplasia (MIN) were obtained. MIN is believed to be similar to human ductal carcinoma in situ (DCIS) and is considered a precursor of invasive tumors. Images were serially obtained from 10-21 weeks of age at 2-3 week intervals. MIN lesions were identified based on their morphology on MR images. Lesions were followed over time and several lesion features were measured including volume, growth rate and morphology. For those MIN lesions that progressed to invasive cancer the progression time was measured.

Results

Overall, 21 MIN lesions were initially detected at an average initial volume of 0.3 ± 0.2 mm³ with an average growth rate of -0.15 ± 0.66 week^-1. Even though all mice were inbred to express the SV40 Tag transgene in the mammary epithelium and expected to develop invasive carcinoma, the individual MIN lesions took vastly different progression paths: (i) 9 lesions progressed to invasive tumors with an average progression time of 4.6 ± 1.9 weeks; (ii) 2 lesions regressed, i.e., were not detected on future images; and (iii) 5 were stable for over 8 weeks, and were demonstrated by a statistical model to represent indolent disease.

Conclusions

To our knowledge, the results reported here are the first measurements of the timescale and characteristics of progression from in situ neoplasia to invasive carcinoma and provide image-based evidence that DCIS may be a non-obligate precursor lesion with highly variable outcomes. In addition, this study represents a first step towards developing methods of image acquisition for identifying radiological characteristics that might predict which in situ neoplasias will become invasive cancers and which are unlikely to progress.

Role of prolactin and vasoinhibins in the regulation of vascular function in mammary gland

The formation of new blood vessels has become a major focus of mammary gland research stimulated by the therapeutic opportunities of controlling angiogenesis in breast cancer. Normal growth and involution of the mammary gland are profoundly affected by the expansion and regression of blood vessels, whereas dysregulation of angiogenesis is characteristic of breast cancer growth and metastasis. Prolactin stimulates the growth and differentiation of the mammary gland under normal conditions, but its role in breast cancer is controversial. Its action is complicated by the fact that prolactin itself is angiogenic, but proteases cleave prolactin to generate vasoinhibins, a family of peptides that act on endothelial cells to suppress angiogenesis and vasodilation and to promote apoptosis-mediated vascular regression. This review summarizes our current knowledge about the vascular effects of prolactin and the generation and action of vasoinhibins, and discusses their possible contribution to the regulation of blood vessels in the normal and malignant mammary gland.

Macrophages regulate the angiogenic switch in a mouse model of breast cancer

The development of a tumor vasculature or access to the host vasculature is a crucial step for the survival and metastasis of malignant tumors. Although therapeutic strategies attempting to inhibit this step during tumor development are being developed, the biological regulation of this process is still largely unknown. Using a transgenic mouse susceptible to mammary cancer, PyMT mice, we have characterized the development of the vasculature in mammary tumors during their progression to malignancy. We show that the onset of the angiogenic switch, identified as the formation of a high-density vessel network, is closely associated with the transition to malignancy. More importantly, both the angiogenic switch and the progression to malignancy are regulated by infiltrated macrophages in the primary mammary tumors. Inhibition of the macrophage infiltration into the tumor delayed the angiogenic switch and malignant transition whereas genetic restoration of the macrophage population specifically in these tumors rescued the vessel phenotype. Furthermore, premature induction of macrophage infiltration into premalignant lesions promoted an early onset of the angiogenic switch independent of tumor progression. Taken together, this study shows that tumor-associated macrophages play a key role in promoting tumor angiogenesis, an essential step in the tumor progression to malignancy.

Effects of the tumor microenvironment on the efficacy of tumor immunotherapy

Cancer immunotherapy utilizes vaccines targeting tumor antigens or tumor endothelium to prevent or regress tumors. Many cancer vaccines are designed to induce antigen-specific effector T cells that migrate to the tumor site. In an optimal situation, the effector T cells penetrate the tumor, release their effector molecules, induce tumor cell death and tumor regression. However, the tumor microenvironment is frequently immunosuppressive and contributes to a state of immune ignorance, impacting on the vaccine's ability to break tolerance to tumor antigen/s. This review discusses the factors in the tumor microenvironment that can affect the efficacy of cancer vaccines. In particular, the review focuses on pathways leading to effector T cell penetration of tumors or the inhibition of this process.

Endostatin therapy reveals a U-shaped curve for antitumor activity

Developing continuous systemic delivery of endostatin has been a goal of many laboratories. We have employed a method of gene therapy utilizing different viral constructs. Here, we report that a new serotype of adeno-associated viruses, which incorporates canine endostatin, provides dose-dependent transgene expression in the circulation after intramuscular injection in mice. Elevated levels of endostatin remained stable in the circulation for at least 4 months. In vitro assays determined that the protein expressed was biologically active. Antitumor activities of the above construct demonstrated a U-shape curve, where the maximum activity was observed within a certain critical concentration range. These data suggest that an optimum dose range may be required to achieve therapeutic efficacy in large animal models.

Adeno-associated virus-mediated delivery of a mutant endostatin in combination with carboplatin treatment inhibits orthotopic growth of ovarian cancer and improves long-term survival

A human ovarian cancer cell line, which migrates to mouse ovaries and establishes peritoneal carcinomatosis, was used to evaluate the cooperative effect of an antiangiogenic gene therapy combined with chemotherapy. The ovarian carcinoma cell line MA148 was genetically modified by "Sleeping Beauty" transposon-mediated delivery of DsRed2 fluorescent protein. Stable, high-level expression of DsRed protein enabled in vivo imaging of peritoneal dissemination of ovarian cancer. Both external and internal imaging, along with histopathology, showed migration of i.p. injected human ovarian cancer cell line to mouse ovaries. Using this model, we evaluated the effect of adeno-associated virus (AAV)-mediated expression of a mutant endostatin either alone or in combination with carboplatin treatment. A single i.m. injection of recombinant AAV (rAAV)-mutant human endostatin with P125A substitution (P125A-endostatin) showed sustained expression of mutant endostatin. Antiangiogenic gene therapy inhibited orthotopic growth of ovarian cancer and resulted in 33% long-term tumor-free survival. A single cycle of carboplatin treatment combined with mutant endostatin gene therapy resulted in 60% of the animals remaining tumor free for >200 days, which was significantly better than rAAV-LacZ and/or carboplatin. Combination treatment delayed tumor appearance in 40% of the animals, wherein the residual tumors were smaller in size with limited or no peritoneal metastasis. These studies suggest that AAV-mediated gene therapy of P125A-endostatin in combination with carboplatin is a useful method to inhibit peritoneal dissemination of ovarian carcinoma.

Generation and characterization of a transgenic mouse model for pancreatic cancer

AIM: To generate a SV40Tag transgenic tumor animal model and to study the mechanism underlying tumorigenesis.

METHODS: A mammary gland expression vector containing SV40Tag DNA was generated. Transgene fragments were microinjeted into fertilized eggs of FVB mice. The genetically manipulated embryos were transferred into the oviducts of pseudo-pregnant female mice. PCR and Northern blot analysis were used for genotype analysis of F1 and F2 mice. Transgene expression was detected by RT-PCR and immunohistochemistry.

RESULTS: SV40Tag gene was detected in two lines of transgenic mice. One of them delivered the transgene to F1 and a tumor was found in the pancreas of these mice. RT-PCR and immunohistochemistry showed that SV40Tag gene was expressed in the tumor. Pathological characterization of the transgenic mice demonstrated that the tumor belonged to pancreatic cystic neoplasm.

CONCLUSION: SV40Tag transgenic mouse model can be successfully established. The transgenic mice develop a pancreatic tumor, which can be used for investigation of the molecular mechanism of tumorigenesis in vivo.

Angiogenesis in normal and neoplastic ovaries

Ovarian physiology is intricately connected to hormonally regulated angiogenic response. Recent advances in the post genomic revolution have significantly impacted our understanding of ovarian function. In an angiogenesis perspective, the ovary offers a unique opportunity to unravel the molecular orchestration of blood vessel development and regression under normal conditions. A majority of ovarian cancers develop from the single layer of epithelium surrounding the ovaries. Angiogenesis is critical for the development of ovarian cancer and its peritoneal dissemination. The present review summarizes recent findings on the angiogenic response in neoplastic ovaries and discusses the prospects of using anti-angiogenic approaches to treat ovarian cancer.

Inhibition of VEGF receptors significantly impairs mammary cancer growth in C3(1)/Tag transgenic mice through antiangiogenic and non-antiangiogenic mechanisms

Cancer growth and progression is often critically influenced by the production of vascular endothelial growth factor (VEGF), a key mediator of angiogenesis. VEGF produced by tumor cells stimulates endothelial cell growth through the binding and activation of the KDR/Flk-1 receptor (VEGFR-2) on endothelial cells. Recently, some human breast cancer epithelial cells have been shown to express VEGF receptors, suggesting a potential autocrine-mediated growth stimulation of a subset of cancers by VEGF. We demonstrate that mammary tumors in the C3(1)/Tag transgenic model express VEGF and VEGF receptors and tumor growth is stimulated by this autocrine mechanism. GW654652, an indazolylpyrimidine, is a VEGFRs tyrosine kinase inhibitor that dramatically reduces both angiogenesis and tumor cell growth in this model, as demonstrated using both in vitro and in vivo assays. GW654652 significantly decreased cell proliferation and induced apoptosis in human umbilical vein endothelial cells and M6 mammary tumor cells derived from C3(1)/Tag (Tag: simian virus 40 T-antigen) transgenic mice. A 75% reduction in VEGF-induced angiogenesis was observed with GW654652 using the chick chorioallantoic membrane assay, whereas GW654652 produced an approximately 85% reduction in angiogenesis as assessed by the Matrigel plug assay. A profound inhibitory effect on tumor growth in the C3(1)/Tag transgenic model of human breast cancer was observed with oral administration of GW654652 as measured by delayed tumor onset, decreased multiplicity, reduced tumor volume, and extended animal survival. The antitumor effects of GW654652 were associated with reduced tumor vascularization and no apparent toxicity. Tumor growth, however, rapidly advanced following cessation of treatment. This is the first demonstration that a VEGF receptor inhibitor, GW654652, has a strong inhibitory effect on angiogenesis and tumor progression in a transgenic model of mammary cancer, suggesting that this is a useful approach for preclinical testing of such agents.

The promise of genetically engineered mice for cancer prevention studies

Sophisticated genetic technologies have led to the development of mouse models of human cancers that recapitulate important features of human oncogenesis. Many of these genetically engineered mouse models promise to be very relevant and relatively rapid systems for determining the efficacy of chemopreventive agents and their mechanisms of action. The validation of such models for chemoprevention will help the selection of appropriate agents for large-scale clinical trials and allow the testing of combination therapies.

Oncolytic Herpes Simplex Virus Vector Therapy of Breast Cancer in C3(1)/SV40 T-antigen Transgenic Mice

Oncolytic herpes simplex virus vectors are a promising strategy for cancer therapy, as direct cytotoxic agents, inducers of antitumor immune responses, and as expressers of anticancer genes. Progress is dependent upon representative preclinical models to evaluate therapy. In this study, two families of oncolytic herpes simplex virus vectors (G207 and NV1020 series) that have been in clinical trials were examined for the treatment of breast cancer, using the C3(1)/T-Ag transgenic mouse model. Female mice spontaneously develop mammary carcinomas, and the C3(1)/T-Ag-derived tumor cell line M6c forms implantable tumors. Both in vitro and in vivo, G47Delta, derived from G207 by deletion of ICP47 and the US11 promoter, was more efficacious than G207. Whereas NV1023, derived from NV1020 by deletion of ICP47 and insertion of LacZ, was as cytotoxic to M6c cells in vitro as G47Delta, it did not inhibit the growth of s.c. M6c tumors but did extend the survival of intracerebral tumor bearing mice. In contrast, NV1042, NV1023 expressing interleukin 12, inhibited s.c. M6c tumor growth to a similar extent as G47Delta, but was less effective than NV1023 in intracerebral tumors. In the spontaneously arising mammary tumor model, when only the first arising tumor per mouse was treated, G47Delta inhibited the growth of a subset of tumors, and when all tumors were treated, G47Delta significantly delayed tumor progression. When the first mammary tumor was treated and the remaining mammary glands removed, NV1042 was more efficacious than G47Delta at inhibiting the growth and progression of injected tumors.

Adeno-associated virus-mediated delivery of a mutant endostatin suppresses ovarian carcinoma growth in mice

Earlier studies have shown that a point mutation in human endostatin at position 125 (human endostatin wherein proline 125 was substituted with alanine, P125A-endostatin) improves endothelial cell binding and antiangiogenic activity. In the present study, we investigated the effect of recombinant adeno-associated virus (rAAV)-mediated gene delivery of P125A-endostatin (rAAV-P125Aendo) in a mouse model of ovarian carcinoma. Intramuscular (i.m.) injection of rAAV-P125Aendo resulted in a dose-dependent increase in serum endostatin levels. Consequently, vascular endothelial growth factor- and basic fibroblast growth factor-mediated angiogenesis was significantly inhibited in mice injected with rAAV-P125Aendo as compared to control mice injected with rAAV-LacZ. Furthermore, gene therapy using rAAV-P125Aendo construct showed sustained secretion of P125A-endostatin for up to 9 weeks after a single i.m. administration. Recombinant AAV-P125Aendo injection significantly inhibited the growth of human ovarian cancer cells in athymic nude mice. Immunofluorescence studies of residual tumors surgically removed from the rAAV-P125Aendo-treated animals showed decreased number of vessel ends and vessel length, indicating inhibition of angiogenesis. These studies suggest that recombinant AAV-mediated antiangiogenic gene therapy methods can be used to inhibit ovarian cancer growth.

A role for antiangiogenic therapy in breast cancer

The success of the angiogenesis inhibitor bevacizumab, the vascular endothelial growth factor antagonist that was recently shown to significantly improve the survival of patients with metastatic colon cancer when administered in combination with conventional chemotherapy, has provided proof of principle in clinical trials that antiangiogenesis can be an important strategy in the treatment of cancer. This report reviews the contemporary therapeutic approaches for breast cancer, the essential role that angiogenesis plays in the initiation and progression of this disease, and the strategies that should be considered to make antiangiogenic therapy a successful component of breast cancer treatment.

VEGF-DT385 toxin conjugate inhibits mammary adenocarcinoma development in a transgenic mouse model of spontaneous tumorigenesis

Previous experiments have shown that a vascular endothelial growth factor (VEGF)-DT385 toxin conjugate inhibits endothelial cell proliferation, angiogenesis and solid tumor growth in a xenotransplant model system. Here, we report that VEGF-DT385 toxin conjugate effectively inhibits spontaneous tumorigenesis. The C3(1)/SV40 TAg transgenic mouse model of mammary gland carcinogenesis was used to determine the effectiveness of VEGF-DT385 toxin conjugate in delaying the onset of disease and the development of solid tumors. Animals were treated daily with conjugate for a period of 7 days. Therapy was initiated at week 14 of development before any visible adenocarcinomas were evident. Treatment of mice with VEGF-DT385 toxin conjugate significantly delayed the onset of tumorigenesis and inhibited solid tumor growth by more than 92%. Furthermore, conjugate treated animals showed less than twice the number of tumor nodules when compared to control mice. Finally, this vascular targeting agent significantly increased survival time of animals by 5 weeks. VEGF-DT385 toxin conjugate resulted in temporary weight loss and no long-lasting toxicity was seen. More importantly, using this established tumor model, VEGF-DT385 toxin conjugate appeared to be as effective as a similar treatment schedule with recombinant human endostatin. Our results suggest that VEGF-DT385 toxin conjugate is a potent inhibitor of mammary adenocarcinoma growth and might be useful in breast cancer therapy.

Improved biological activity of a mutant endostatin containing a single amino-acid substitution

Human endostatin has an internal Asn-Gly-Arg (NGR) motif at position 126–128 following a proline at position 125. Asn-Gly-Arg-containing peptides have been shown to target tumour vasculature and inhibit aminopeptidase N activity. We previously compared the in vitro and in vivo biological activities of native endostatin and endostatin with a proline to alanine mutation (P125A-endostatin). P125A-endostatin exhibited greater inhibition of both endothelial cell proliferation and human ovarian cancer growth compared to native endostatin. Here we explore further the effects on biological activity of the P125A mutation, and show that aminopeptidase N is not involved. To determine whether the increased biological activity of the mutant was due to unmasking of downstream NGR-sequence, effect of endostatin on aminopeptidase N activity was investigated. Neither the native nor the P125A-endostatin inhibited aminopeptidase N. However, synthetic peptides consisting of the S118-T131 region of endostatin inhibited aminopeptidase N. These results suggest that the internal NGR site in native or mutant endostatin is not accessible to aminopeptidase N, and that this activity is not involved in the enhanced biological activity of the P125A form. P125A-endostatin bound to endothelial cells more efficiently than native endostatin and exhibited greater inhibition of not only proliferation but also migration of endothelial cells. P125A-endostatin also localised into tumour tissue to a higher degree than the native protein, and displayed greater inhibition of growth of colon cancer in athymic mice. Both proteins inhibited tumour cell-induced angiogenesis effectively. Real-time PCR analysis showed that both native and P125A-endostatin decreased expression of key proangiogenic growth factors. Vascular endothelial growth factor and angiopoietin 1 were downregulated more by the mutant. These studies suggest that the region around P125 can be modified to improve the biological activity of endostatin.

Anti-angiogenic therapy in breast cancer

Breast cancer is a worldwide epidemic among women, and one of the most rapidly increasing cancers. Not only the incidence rate but also the death rate is increasing. Despite enthusiastic efforts in early diagnosis, aggressive surgical treatment and application of additional non-operative modalities, its prognosis is still dismal. This emphasizes the necessity to develop new measures and strategies for its prevention. The understanding of the biology of angiogenesis is improving rapidly, offering the hope for more specific vascular targeting of tumor neovasculature. Anti-angiogenic therapy is a promising, relatively new form of cancer treatment using drugs called angiogenesis inhibitors that specifically inhibit new blood vessel growth. Extensive studies conducted over the past few years have recognized that overexpression of COX-2, VEGF in the cancer might be the leading factors, can induce angiogenesis via induction of multiple pro-angiogenic regulators. Breast tumor growth and metastasization are both hormone-sensitive and angiogenesis-dependent. A single angiogenic inhibitor is not capable to inhibit angiogenesis. Therefore, we should select a combination of angiogenesis inhibitors targeting COX-2, VEGF, and bFGF pathway. This article reviews the background and implementation of the current use of angiogenesis inhibitors and discusses the likely therapeutic roles in the early and advanced breast cancer together with its potential for chemoprevention.

Addition of integrin binding sequence to a mutant human endostatin improves inhibition of tumor growth

Tumor vasculatures express high levels of alphaVbeta3/alphaVbeta5 and alpha5beta1 integrins. Consequently, peptides containing the RGD (Arg-Gly-Asp) sequence, which is present in ligands of integrins, is effective in targeting therapeutic reagents to tumor vascular endothelium. In our study, we investigated whether the biologic activity of endostatin can be enhanced by the addition of an integrin targeting sequence. RGD sequence was added to either the amino or carboxyl terminus of endostatin containing a point mutation, P125A-endostatin. Earlier we have shown that the P125A mutation did not affect the biologic activity of endostatin but in fact had better antiangiogenic activity when compared to the native molecule. Further modification of P125A-endostatin with the RGD motif showed specific and increased binding to endothelial cells, and the increased binding coincided with improved antiangiogenic properties. Both amino and carboxyl terminal RGD-modification of P125A-endostatin resulted in greater inhibition of endothelial cell migration and proliferation. RGD modification increased tumor localization without affecting the circulatory half-life of P125A-endostatin, and RGD-modified P125A-endostatin was found to be more effective when compared to the P125A-endostatin in inhibiting ovarian and colon cancer growth in athymic mice. Complete inhibition of ovarian tumor growth was observed when P125A-endostatin-RGD was encapsulated into alginate beads. These studies demonstrate that addition of a vascular targeting sequence can enhance the biologic activity of an antiangiogenic molecule.

Selective stimulation of VEGFR-1 prevents oxygen-induced retinal vascular degeneration in retinopathy of prematurity

Oxygen administration to immature neonates suppresses VEGF-A expression in the retina, resulting in the catastrophic vessel loss that initiates retinopathy of prematurity. To investigate the mechanisms responsible for survival of blood vessels in the developing retina, we characterized two VEGF-A receptors, VEGF receptor-1 (VEGFR-1, also known as Flt-1) and VEGF receptor-2 (VEGFR-2, also known as Flk-1). Surprisingly, these two VEGF-A receptors differed markedly during normal retinal development in mice. At 5 days postpartum (P5), VEGFR-1 protein was colocalized with retinal vessels, whereas VEGFR-2 was detected only in the neural retina. Real-time RT-PCR identified a 60-fold induction of VEGFR-1 mRNA in retina from P3 (early vascularization) to P26 (fully vascularized), and no significant change in VEGFR-2 mRNA expression. Placental growth factor-1 (PlGF-1), which exclusively binds VEGFR-1, decreased hyperoxia-induced retinal vaso-obliteration from 22.2% to 5.1%, whereas VEGF-E, which exclusively binds VEGFR-2, had no effect on blood vessel survival. Importantly, under the same conditions, PlGF-1 did not increase vasoproliferation during (a). normal vessel growth, (b). revascularization following hyperoxia-induced ischemia, or (c). the vasoproliferative phase, indicating a selective function supporting blood vessel survival. We conclude that VEGFR-1 is critical in maintaining the vasculature of the neonatal retina, and that activation of VEGFR-1 by PlGF-1 is a selective strategy for preventing oxygen-induced retinal ischemia without provoking retinal neovascularization.

The use of genetically altered mice for breast cancer prevention studies

Chemoprevention through nutritional and dietary changes may offer an important means of inhibiting the development and progression of breast cancer, which would have a major impact on public health. Studies to assess the efficacy of potential chemopreventive compounds are difficult to perform in large human populations, whereas the use of genetically engineered mice (GEM) for preclinical testing offers several advantages. GEM models can be utilized to assess the inhibitory effects of nutritional and chemopreventive agents on well-defined oncogenic signaling pathways. Because several transgenic mouse models progress through a well-defined temporal series of stages leading to invasive carcinoma formation, they may be particularly useful for determining cancer stage-specific responses to nutritional and chemopreventive agents. The C3(1)SV40 T/t-antigen transgenic mouse mammary cancer model has been utilized for chemopreventive research in which mammary tumors develop over a well-characterized time course. Several compounds have been shown to inhibit mammary tumor development in this model, including retinoids, di-fluoromethylornithine (DFMO), dehydroepiandrosterone (DHEA), antiangiogenic compounds and nonsteroidal antiinflammatory drugs (NSAID). All of the chemopreventive agents used in the C3(1)Tag mammary mouse model appear to affect the promotion stage of tumorigenesis, suggesting that these agents may be useful in inhibiting the transition of human ductal carcinoma in situ (DCIS) to invasive carcinoma. Selective combinations of chemopreventive agents may be particularly useful for targeting multiple signaling pathways involved in cancer development and progression leading to improved clinical responses. The application of gene expression profiling to chemopreventive studies will aid in the selection of appropriate models for preclinical testing and further define mechanisms of action.

Endostatin action and intracellular signaling: beta-catenin as a potential target?

Endostatin, the C-terminal part of collagen XVIII, has been shown to inhibit blood vessel formation in different pathological conditions characterized by increased angiogenesis, such as growing tumors. Subcutaneous injection of endostatin in tumor-bearing mice leads to decreased tumor growth, and even in some cases, cure of tumor disease. Endostatin has been tested in a clinical phase I study and shown not to be toxic. Whether the finding in mice that endostatin treatment does not result in development of resistance will hold true in humans is too early to tell. Endostatin binds to a specific motif in heparan sulfate, which may serve a co-receptor function. The structure of a potential primary receptor is not known. The mechanism of action of endostatin in inhibition of angiogenesis and thereby, inhibition of tumor growth, involves apoptosis of tumor cells. The most consistent effect of endostatin on endothelial cells in vitro is inhibition of endothelial cell migration, which may be due to disturbed cell-matrix interactions. An interesting candidate for transducing endostatin's effect on apoptosis and cell migration is beta-catenin, an intracellular protein which participates both in cell adhesion and in transcriptional regulation.

Pre-clinical applications of transgenic mouse mammary cancer models

Breast cancer is a leading cause of cancer morbidity and mortality. Given that the majority of human breast cancers appear to be due to non-genetic factors, identifying agents and mechanisms of prevention is key to lowering the incidence of cancer. Genetically engineered mouse models of mammary cancer have been important in elucidating molecular pathways and signaling events associated with the initiation, promotion, and the progression of cancer. Since several transgenic mammary models of human breast cancer progress through well-defined cancer stages, they are useful pre-clinical systems to test the efficacy of chemopreventive and chemotherapeutic agents. This review outlines several oncogenic pathways through which mammary cancer can be induced in transgenic models and describes several types of preventive and therapeutic agents that have been tested in transgenic models of mammary cancer. The effectiveness of farnesyl inhibitors, aromatase inhibitors, differentiating agents, polyamine inhibitors, anti-angiogenic inhibitors, and immunotherapeutic compounds including vaccines have been evaluated in reducing mammary cancer and tumor progression in transgenic models.